1. Field of the Invention
The present invention relates to a radio frequency identification system that is capable of preventing signal collision, in particular, to a radio frequency identification system with multi-band transmission for preventing signal collision.
2. Related Art
A radio frequency identification (RFID) system is an advanced technology that identifies an object by transmitting data through radio frequency and generally consists of an RFID tag and an RFID reader.
In certain applications, the RFID reader may need to read multiple RFID tags at the same time and such a situation often leads to collision of tag signals. The readability of tag signals can be enhanced if the RFID tags are read one by one. However, it is often that a number of RFID pass by an RFID reader at the same time, and in such a situation, it becomes vitally important to properly handle collision of tag signals.
Signal collision occurring in an RFID system can be classified as two categories, namely tag signal collision and reader signal collision. The former represents the situation where a RFID reader simultaneously receives signals returned from a number of RFID tags, leading to imprecise receiving of signals or incorrect result of reading, while the later indicates the situation where interference is caused by a tag receiving instructions from a number of readers at the same time. Signal collision simply results in failure and/or missing of signal transmission, or even leads to incorrect data due to incorrect reading of signals, both being hindering the operation of correct identification.
The state-of-art solution for handling signal collision occurring in RFID tag transmission is the so-called time division multiple access (TDMA), wherein RFID readers are controlled to carry out signal transmission at different time points. However, such a solution is only good for RFID systems that are comprised of RFID readers of small numbers and once the number of the RFID readers installed reaches an upper limit, the reliability and performance of the system get lowered due to over division of time within a given time period.